I had a similar problem, though on a different type of tap but the fixing arrangement looks similar. I tried WD40 to no avail, freezer spray, hot air gun, alternate heating/freezing etc - all worth a try but no success. Having run out of patience I clamped the tap in my workbench (a vice would work but be sure to protect the chrome finish) and used a large screwdriver and hammer to force the handle off. There was slight damage but only superficial. The problem was corrosion caused by two dissimilar metals in contact with each other in a damp environment. Once separated and cleaned up, I reassembled with a dab of grease on the mounting stud to facilitate easier removal if needed in future.
Hope this helps!